Decades of study on volcanic arcs have provided insight into the overarching processes that control magmatism, and how these processes manifest at individual volcanoes.
However, the causes of ubiquitous and dramatic intra-arc variations in volcanic flux and composition remain largely unresolved.
Magmatism plays an important role in establishing the composition and architecture of the crust in subduction zones via addition of mass and heat, as well as crustal melting, metamorphism, and hydrothermal alteration.
These processes will in turn influence the broad-scale geophysical properties of the crust, such as surface heat flow and seismic velocities, which can then be used to constrain broad-scale magmatic processes.
Here we show that along-strike volcanic variability in the Quaternary Cascades Arc is primarily related to variations in the flux of basalt into the crust, rather than variations in their crustal storage history.
This approach shows promise for studying other large-scale frontier geologic problems in volcanic arcs.These hypotheses, used either explicitly or implicitly, have been in place for decades, but there remains little clear consensus about the relative contribution of the crust and mantle in producing volcanic diversity.Schematic figure of the possible mantle and crustal roles in forming arc volcanic diversity.We believe that the potential causes of volcanic diversity in arcs can be framed as two end-member hypotheses (Fig. In the first, the observed variations in arc volcanism are produced solely by differences in crustal processes and properties, with constant mantle flux along strike.Alternatively, variations in volcanic fluxes and compositions are primarily the result of differences in the underlying mantle flux (controlled in turn by variations in the downgoing slab and/or mantle wedge), with processes within the arc crust playing only a secondary role.The result is that geochemical and petrological datasets are hard to reconcile and compare with the regional and integrative datasets produced by many geophysical studies, and this leads to qualitative, rather than quantitative comparisons.Finally, understanding of the larger-scale controls on volcanism and magmatism is also limited by the common approach of focusing on only one part of the subduction system (e.g., upper crust or mantle wedge), with very limited consideration of the feedbacks and interactions that occur across the entire arc system.Thus, understanding how subduction can produce a volcanic record that is highly episodic and heterogeneous in space and time is an extant grand challenge for subduction science.Furthermore, resolving the ultimate controls over the causes of volcanic and magmatic diversity in arcs has important ramifications for understanding the dynamics of continental margins, mantle flow behavior, and volcanic hazards.Our approach suggests that the mantle is the primary driver of volcanic arc diversity in the Cascades.We can potentially link the observed volcanic record in a volcanic arc with regional geophysical datasets by exploring the thermal effects of magmatism on the crust and mantle.